Biometrics authentication apparatus for performing personal authentication by the use of human physical characteristics are widely used in security systems in which entering and leaving a room are managed. Fingerprints, irises in pupils, palm or finger veins, voiceprints, features and the like are used as physical characteristics. Authentication performed by the use of these physical characteristics has been put to practical use. There are a large number of palm or finger veins. Their patterns are complex and do not change for life. In addition, they are organs in a body which are difficult to forge. Accordingly, among others palm or finger veins are suitable for personal authentication.
With vein authentication the characteristics of hemoglobin in each red blood cell included in blood are used. That is to say, hemoglobin in each red blood cell which runs through an artery is combined with oxygen and is oxyhemoglobin. In a vein this oxyhemoglobin changes to deoxyhemoglobin which is not combined with oxygen. It is a characteristic of the deoxyhemoglobin that the deoxyhemoglobin absorbs near-infrared rays with a wavelength close to 760 nm. Accordingly, if a palm is irradiated with near-infrared rays and an image is produced from light reflected therefrom, then the image in which vein portions are black is obtained. The reason for this is that the intensity of light reflected from the vein portions is low.
A biometrics authentication apparatus registers in advance an image obtained in this way in a living body information database as living body information. When authentication is necessary, the biometrics authentication apparatus compares an image newly captured with registered living body information and confirms the identity of a person. At this time the biometrics authentication apparatus compares the image newly captured with the registered living body information one by one. After the biometrics authentication apparatus finishes comparing the image newly captured with all of the registered living body information, the biometrics authentication apparatus confirms the identity of a person on the basis of whether a degree of similarity between the image newly captured and each piece of registered living body information is greater than or equal to a determined value.
The data amount of living body information, such as a captured image, is very large, so it takes a long time to perform a comparison process one by one. Time taken to confirm the identity of a person lengthens with an increase in the number of pieces of registered living body information. In order to reduce wait time before completion of authentication, it is necessary to limit the number of pieces of registered living body information. Furthermore, in order to increase the number of pieces of registered living body information, it is necessary to prepare a plurality of biometrics authentication apparatus in each of which the number of pieces of registered living body information is limited.
This is what is called a one-to-N authentication process. A biometrics authentication apparatus which performs a one-to-N authentication process, which can reduce comparison time, and which can increase the number of pieces of registered living body information was proposed (see, for example, Japanese Laid-open Patent Publication No. 2007-249339). With this biometrics authentication apparatus vein characteristic amounts which are generated from captured images and the data amount of which is small and vein data for the captured images are registered in advance. When the biometrics authentication apparatus makes comparison, the biometrics authentication apparatus first calculates scores indicative of rough degrees of similarity from vein characteristic amounts generated from a captured image and the registered vein characteristic amounts, and determines the order of comparison according to a result of sorting the scores. The biometrics authentication apparatus then treats only vein data which ranks high in the order of comparison as an object of comparison and performs a detailed comparison process. As a result, the biometrics authentication apparatus makes a time-consuming comparison not for all registered living body information but for only registered living body information narrowed down to some degree. This significantly reduces comparison time. This reduction in comparison time enables an increase in the maximum number N of pieces of living body information which can be registered. In addition, this biometrics authentication apparatus uses a frequency component indicative of whether vein patterns are sparse or dense, an angle component indicative of the direction of a vein pattern, and a curvature component indicative of the direction of a curvature of a vein pattern as vein characteristic amounts for narrowing down an object of comparison.
The above biometrics authentication apparatus determines the order of comparison on the basis of the three vein characteristic amounts. However, the accuracy of the vein characteristic amounts is low, so it is impossible to increase the probability that vein data for which a degree of similarity is high will rank high in the order of comparison. Accordingly, the maximum number of pieces of living body information which can be registered cannot be increased.